Sunday, February 22, 2015

Hi everyone, so this is my first post for 2015, in my last post I made a tutorial of how to prepare a sand mould using a solid pattern. In this post I will explain how I made a solid aluminum boat cleat using a split pattern with my homemade furnace.
I have also created another tutorial this time explaining how to create the split pattern for this type of aluminum casting.

This special request came from my brother that is taking a course in becoming a yacht skipper.

He doesn't have a Yacht yet.... but a boat cleat is a good start ;-)
So first I have made a quick sketch design using Google Sketchup.

After I had some idea and plan as to how I want the pattern to look like I started making it using MDF as the main material for the pattern. The split pattern is constructed from 2 half's of 18mm MDF.

The pattern size is 100mm height, 300mm width & 36mm in depth. I started by making a template of the boat cleat transferring it to a sheet of 8mm MDF, once I had the template and the desired shape cut with a jigsaw I used the template as a guide for my electric router, I transferred the boat cleat shape into the 2 parts of MDF by using the template. As I did not have a long enough straight bit for my router (+36mm) I used 2 bits, a short straight bit and a flush trim bit with bearing running it around the template. It took a bit longer but the end result was satisfying and accurate.

(Just a quick note as how I connected the 2 split parts, I connected the 2 parts of MDF with small pins making sure they will not be in the way of the router bit. )

After the pattern was complete the same pins are used to align the 2 half's when placed into the foundry flask, it is very important to make sure that the 2 parts are aligned accurately for a good aluminum casting results.

Next step after creating the boat cleat pattern from the MDF : I used my table router to round all the corners and create a groove in the MDF pattern giving it a depth and much more of a 3D attractive look.

In the next images you can see the stages and the different bits that I have used for the table router.

MDF is a great and easy material to shape, however as it is made from medium density fiber there are a few important highlights: 1st - its important to work with dust extractor and a good mask avoiding inhalation of the MDF dust. 2nd - as MDF has very rough edges when being cut it is important to seal the MDF pattern, I used a wood filler to improve the angle (Draft's) of the pattern and after the wood filler was dry I sanded the MDF pattern using different grades of sand paper until a smooth finishing was achieved. Last thing that I did was coating the pattern with gloss varnish, I had concerns that I will not be able to separate the 2 half's as I varnished the pattern with the 2 half's connected but to my surprise it was very easy to separate between the two sides and from this point the pattern was ready to be used for the sand mould.

At this point the split pattern was ready after adding 2 coats of varnish, the surface was glossy and smooth, I made the sand mould using a wooden flask & oil bonded sand for a good finishing. I did have some concerns that the sand mould might break around the straight sections of the pattern but the sand mould turned out very well with minor damages when I removed the split pattern.

After removing the split pattern from the sand mould I created the gating system in the sand, a poor gating system can lead to casting defects so this is a very important stage when preparing the sand mould, once the gating system is complete it is ready to be filled with molten aluminum.

Next I closed and clamped the flask and started to heat my homemade furnace, after the aluminum was in a molten stage I poured it into the flask and opened it after 1 hour, the solid aluminum boat cleat turned out very well with minor imperfections that were very easy to clean and fix.

In the next set of images you can see the solid aluminum boat cleat after taking it out from the sand mould. I used a reciprocating saw with a metal blade to quickly cut off the risers. Last part was to clean the aluminum casting and give it a light polish.

Here is my tutorial video with most of the steps, creation of the sand mould and the actual molten aluminum pouring creating the solid aluminum boat cleat, enjoy:

This is just a follow up post for my aluminum foundry flask casting progress. The first four parts of my flask cope are casted, at this st...

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